1. Field of the Invention
The present invention relates to serial electrophotographic apparatuses, and more particularly to a serial electrophotographic apparatus in which a latent image is formed on a recording drum, and toner is used to print a visible image on recording paper.
A demand for inexpensive and compact electrophotographic apparatuses has resulted in the development of serial electrophotographic printers. In electrophotographic printers, a carriage for carrying a printhead is capable of performing an electrophotographic process. In these electrophotographic printers, recording paper is transported on a transferring unit in a direction perpendicular to a direction in which the carriage is translated so that the transferring unit effects an image transfer onto the recording paper. A roller-shaped fixing unit disposed ahead of the carriage in the direction of transportation effects fixing. In serial electrophotographic printers, improvement in printing quality is requested.
2. Description of the Prior Art
FIGS. 1A and 1B show a constitution of a conventional serial electrophotographic printer 11, FIG. 1A being a partial top view of the printer, and FIG. 1B being a cross-sectional view of a carriage.
The serial electrophotographic printer 11 shown in FIGS. 1A and 1B is disclosed in Japanese Laid-Open Patent Application Ser. No. 61-152463. In the electrophotographic printer 11, a shaft 14 is disposed parallel with rollers 13a and 13b for transporting recording paper 12. A carriage 15 is driven by a motor (not shown) and guided by the shaft 14 to be movable in a direction perpendicular to a direction in which the recording paper is transported. A fixing unit 16 longer than the width of the recording paper 12 is fixed ahead of the carriage 15 in the direction in which the recording paper is transported. A transferring unit 17 is disposed below the recording paper 12 to lie in the direction in which the carriage 15 is transported.
The carriage 15 carries an image carrying body (recording drum) 21 which is rotated at a peripheral speed synchronized with the movement of the carriage 15. The surface of the image carrying body 21 is uniformly charged by a charger (a charging roller) 22, and an electrostatic latent image is formed by an exposer 23. The electrostatic latent image is made visible to become a toner image by a developing roller 26 which is formed adjacent to the image carrying body 21 and supplies toner 25 stored in a developing unit 24 to the image carrying body 21. The toner image formed on the image carrying body 21 is transferred to the recording paper 12 by the transferring unit 17 disposed opposite to the image carrying body 21, the recording paper 12 being led through a space between the image carrying body 21 and the transferring unit 17. The recording paper 12 is transported so that a part which has undergone a transferring process faces the fixing unit 16, whereupon the image is fixed.
The toner 25 is formed, for example, by mixing iron powder with plastic powder having a softening point (melting point) of 100.degree.-150.degree. C. and a diameter of 10-50 .mu.m and painted in a predetermined color. When left in an unchanged condition for a extended period of time, some powders become glued to each other. Hence, it is necessary to shake or stir the toner when it is used.
If the developing unit 24 is filled with the toner 25, it is possible for the developing roller 26 to supply the toner 25 to the recording drum 21 in a stable manner. However, the aforementioned property of the toner 25 may turn the toner 25 into lumps within the developing unit 24 when the quantity of the toner 25 decreases and may invite a problem in that it is impossible to supply the toner 25 to the recording drum 21 in a stable manner, and thus deteriorating printing quality.